1. Field of the Invention
The invention relates to a hydraulic circuit for longwall support by means of a support device (support shield) for use in underground mining.
2. Description of Related Art
Such circuits are well known from PCT/DE2010/000685 (the publication of which is W02011006461A2). The proposed pressure monitoring system prevents unforeseen operating conditions where pressure conditions may occur that are sufficient to manipulate the hydraulic pilot control, i.e. the opening of essential valves even in case of failures to the pumping system, or if in case of an emergency the overall electric and hydraulic control systems are switched off, or in case of extremely high pressures from the rock which the load maintaining valves are not capable of handling.
The arrangement of W02011006461A2 according to one embodiment also monitors the annular piston line for each cylinder/piston assembly by means of a pressure sensor. When a pre-determined maximum pressure is achieved, the entire longwall is depressurized so that particularly the unlocking process for the check valves that retain the rock pressure is disabled. This can, however, cause operating conditions that may require the system to be controlled either manually or automatically.
The purpose of the invention is to design the circuit in such a manner that a comprehensive monitoring of the system as well as any necessary manipulation of the control system is possible.